1. Field of the Invention
The present invention relates to a conveyor trolley comprising a pair of wheels rolling over a flat upper face of an upper end rail portion of a guide rail with one wheel acting as a drive wheel attached to an output shaft of a speed-reducing unit mounted in a trolley body and a motor for driving the output shaft via a speed-reducing mechanism in the speed-reducing unit.
2. Description of the Prior Art
The conveyor trolley of the above-noted type is used as a trolley constituting an electric cart for conveying an object or as a trolley of a tractor electric cart for tracting a cart for conveying an object. In such trolley, it is known to employ a motor having a so-called negative brake such that when power supply is stopped to stop the motor the brake is automatically activated to stop the drive wheel thereby stopping the trolley on a guide rail. For manually moving the trolley, a brake release lever attached to the motor with the brake to release a rotary shaft of the motor from the transmission. However, a speed-reducing mechanism having a considerably large speed reduction ratio provided between the rotary shaft of the motor and an output shaft of the speed-reducing unit provides too great a resistance for the worker to smoothly and easily push the trolley at a convenient speed.
Further, in the trolley of the above-described type, the wheel rolling on the guide rail is attached to the shaft by means of a key or a spline connection. And, for preventing inadvertent disengagement of this wheel in its axial direction, an inner end of a lock bolt screwedly extending radially through a boss of this wheel is placed in pressurized contact with the peripheral face of the shaft, or a wheel-retentive plate is fixed by means of a screw to an outer end of the shaft.
However, if a wheel having a flat peripheral face rolling on the flat upper face of the guide rail is used in place of a wheel having a groove for engaging the upper end portion of the guide rail, when the trolley travels at a horizontal curved passage having its center of arc at the side of the trolley body relative to the guide rail, the wheel is subjected to a very large thrust force in a direction for disengaging the wheel from the shaft. Therefore, with such wheel securing means as described above, there is a danger of the wheel inadvertently disengaging from the shaft as the secured engagement between the wheel and the shaft is gradually loosened because of the thrust force acting on the engagement repeatedly.